1. Technical Field
This disclosure is generally related to solid-state lamps.
2. Description of the Related Art
Fixed intensity lighting has been in use for more than a century. While fixed intensity lighting is useful in many applications, some applications benefit from the ability to control lighting intensity, adjust lighting intensity or synchronize lighting intensity with one or more scheduled events. In one particular application, it may be desirable to adjust the intensity of only a portion of the lighting fixtures or luminaires used in a specific location such as an industrial facility, parking lot, or commercial establishment. Adjusting the intensity of only a portion of the luminaires within a given location enables the use of selective or scheduled lighting scheme. For example, luminaires above a continuously occupied (i.e., 24/7/365) work area may be maintained at maximum intensity at all times, while other luminaires above a periodically occupied work area (e.g., a work area occupied from 9:00 A to 5:00 P Monday through Friday) may be at maximum intensity while the work area is in occupied, and at a lesser intensity level when the work area is unoccupied. In another example, variable intensity luminaires may be desirable in a consumer shopping area where well-lit temporary kiosks or seasonal displays reduce the need for general lighting for limited periods of time in areas surrounding the kiosk or seasonal display.
A single electrical circuit is frequently used to provide power to multiple luminaires thereby limiting the ability to control the intensity of an individual luminaire on the electrical circuit, as a change in any electrical parameter (e.g., a reduction in voltage) will be reflected in ALL of the luminaires coupled to the electric circuit. Additionally, luminaires are frequently mounted at elevations rendering physical access to controls on individual luminaires, impractical, difficult, dangerous, or a combination of all three. Physical access to a luminaire for disconnection, maintenance, or manual adjustment of the intensity of an individual luminaire frequently requires the use of specialized equipment such as a “bucket truck” or self-propelled scissor lift. The need for specialized equipment requires following safety procedures, such as blocking off the work area and posting an additional worker to stand as a look-out, to protect both the maintenance person and any potential customers in the vicinity of the maintenance. Thus, individually adjusting the intensity of each luminaire can be disruptive, time-consuming, and costly.
The use of inexpensive dimmer switches to control the intensity of individual luminaires is possible where incandescent lamps are used. However, the inherent energy inefficiency and relatively short operating life of incandescent lamps is both financially unsound, requiring dimmer control wiring between each luminaire and a dimmer switch, and ecologically wasteful, using inefficient, short-lived, incandescent lamps. Other lamps, for example high efficiency lighting devices, such as metal halide lighting devices, typically cannot be dimmed effectively. Although some metal halide ballasts are configured to permit dimming, such ballasts generally require extensive wiring and control systems to enable dimming.
Other approaches to adjusting the intensity of individual luminaires include manufacturing incandescent lighting devices with multiple incandescent filaments, or installing neutral density filters within lighting devices. Incandescent lighting devices having multiple incandescent filaments typically require connection to a multiple-position switch in order to select one or more of the filaments within the lighting device. Similar to the approach using a wall-mounted dimmer, connecting additional wiring to support use of a multiple-position switch adds hardware and labor costs to the lighting installation. Additionally, installing filters to adjust the output intensity of the lighting device wastes energy by reducing the overall output of the lighting device and suffers from the drawbacks associated with having a person physically elevated to the lighting device to install the filters.